The prolific Al-Hilal striker was handed an eight-match ban by the Asian Football Confederation for the incident, which happened in November after his club were beaten by the Australian side 1-0 over the two legs of the final.
CAS stayed the punishment in March and late on Monday reduced the ban to two matches for the head-butt and four matches for the spitting offence with a further two-match ban suspended for a probationary period of two years.
The original ban, six for the spitting and two for the head-butt, was the minimum Al Shamrani could have received for the offenses.
Gianfranco Zola takes 'calculated risk' with coaching job in Qatar
The AFC had attempted to delay the announcement of their initial verdict to avoid embarrassment when they presented Al Shamrani with their Player of the Year award, only for the news to leak out.
An appeal to the AFC failed but the regional body allowed him to compete in the Asian Cup with Saudi Arabia in January after restricting the ban to just ACL League matches.
Al Shamrani served two matches of the ban before CAS granted the stay and he returned to score his 26th goal in the ACL as Al Hilal beat Iran's Foolad 2-0 earlier this month.
The statement on the CAS website said the full verdict, with the grounds for the reduction in the punishment, would be issued at a later date.
Jalisco stadium closed after fans interrupt match
David Villa scores on debut as New York City FC win home opener at Yankee Stadium